The semiconductor industry utilizes various chemicals for etching materials and for cleaning reaction chambers where semiconductor materials are processed. These etch or clean chemicals are generally divided into two groups, wet chemicals and dry or gaseous chemicals. The semiconductor industry is moving away from the use of wet chemicals because of contamination and handling problems. As the semiconductor industry moves to a greater extent to the utilization of dry chemicals or gaseous chemicals for etching and cleaning operations, the disposal of such chemicals subsequent to use is becoming a significant problem.
In the use of dry gaseous etchant chemicals for etching materials of construction in semiconductor systems or for etching and cleaning reaction chamber walls, tools and surfaces, inevitably, some of the gaseous chemical is not reacted with the contaminants or species to be etched or cleaned, and these unreacted chemicals are removed as an effluent from the reaction chamber along with various reaction by-products formed during the clean or etch. Venting of such etching and/or cleaning chemicals is coming under increasing scrutiny. For instance, exemplary gaseous chemicals used for etching and cleaning include carbontetrafluoride, hexafluoroethane, nitrogen trifluoride and sulfur hexafluoride. As reported in the article "PFCs and the Semiconductor Industry: A Closer Look," by Maroulis, et al., Semiconductor International, November 1994, pp.107-110, these potential gaseous chemical etchants or cleaning agents all have Global Warming Potential (i.e., they induce temperature rise in the earth's atmosphere). Increasingly, governments and international treaties are requiring that the venting of such Global Warming Potential chemicals be reduced or eliminated.
Therefore, within the semiconductor fabrication industry, a need exists for appropriate etching and cleaning chemicals which have acceptable performance for etching and cleaning, but which do not constitute a significant Global Warming Potential when byproducts or unreacted chemical are vented to the atmosphere.
Currently, attempts to resolve the outstanding problem with gaseous etch and clean chemicals fall into one of four categories: (1) attempts to optimize etch and/or clean processes such that less Global Warming Potential chemicals are emitted into the atmosphere, (2) attempts to recycle etch and/or clean chemicals from an exhaust stream so that they can be properly disposed of or reutilized without atmospheric emissions, (3) attempts to abate etch and/or clean chemicals in exhaust streams by chemical reaction or burn boxes which incinerate and render the unreacted etch and/or clean chemical effluents inoffensive, particularly with regard to Global Warming Potential, and (4) lastly, attempts have been made to select or develop various replacement gaseous chemicals for etch and/or clean duty, but at the present time, no acceptable candidates have been identified.
In the article, "Some Chemical Aspects of the Fluorocarbon Plasma Etching of Silicon and Its Compounds," by Coburn, et al., appearing in IBM Journal of Research Development, Vol. 23, No. 1, January 1979, pp 33-41, various etchants were studied for the etch of silicon and silicon dioxide using active gases such as oxygen, hydrogen, nitrogen, water and tetrafluoroethene with carbon tetrafluoride. The article goes on to indicate the applicability of added oxygen gas to traditional gaseous etch chemicals for etching silicon. Oxygen was reported to increase the fluorine to carbon (F/C) ratio because it was identified as an carbon scavenger. The article's conclusion is that it is desirable to have lower F/C ratios for high SiO.sub.2 /Si etch ratios. Etching of silicon with chemicals which contain molecularly bound oxygen was also studied in the experiments on added oxygen, but oxygen was not added to the chemicals with molecularly bound oxygen. Trifluoroacetic anhydride was studied in the plasma etching of silicon as an example of a chemical with molecularly bound oxygen. Trifluoroacetic anhydride was reported to have only "medium" silicon etch rates. The article identifies that it is well recognized that the rate of etch of silicon and silicon dioxide are dissimilar.
Stanley Wolf, et al. in SILICON PROCESSING FOR THE VSLI ERA, Lattice Press, Vol. 1, Process Technology, pp 547-550, also describes the fact that silicon dioxide and silicon have different etch characteristics and etch preferably under different etch chemistry conditions, thus allowing for selectivities represented by the reported SiO.sub.2 /Si etch ratios.
Despite knowledge of the above recited problem with etch chemicals having significant Global Warming Potential and the known use of fluorocarbons for etching generally and etching silicon specifically, particularly the use of trifluoroacetic anhydride to etch silicon, the art has failed to identify gaseous etch and/or clean chemicals which are useful for removing silicon dioxide and silicon nitride from semiconductor materials of construction or plasma reactor chamber walls and surfaces which gaseous etch and/or clean chemicals are effective with regard to etch performance, while at the same time providing a reduction in Global Warming Potential when released as an effluent into the atmosphere. The present invention overcomes the drawbacks of the prior art by utilizing a family of etch and/or clean chemicals having a surprising reactivity or etch and clean performance, while providing low Global Warming Potential for unreacted chemical effluent or reaction by-products, as set forth in greater detail below.